linux-kernel - Re: [PATCH] arm64: kernel: need extern variable 'screen

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Date:	Tue, 21 May 2013 18:13:08 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Will Deacon <will.deacon@....com>
CC:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Tony Lindgren <tony@...mide.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: kernel: need extern variable 'screen_info' for
 related driver using.

On 05/21/2013 05:03 PM, Will Deacon wrote:
> On Tue, May 21, 2013 at 08:51:39AM +0100, Chen Gang wrote:
>> On 05/21/2013 02:57 PM, Geert Uytterhoeven wrote:
>>> On Tue, May 21, 2013 at 5:15 AM, Chen Gang <gang.chen@...anux.com> wrote:
>>>>>>> I think it would be better if we added a something like
>>>>>>> CONFIG_HAVE_VGA_CONSOLE, which VGA_CONSOLE can then depend on. Architectures
>>>>>>> like x86 can then select the former, and we can remove the long list of
>>>>>>> architectures from the current option.
>>>>>
>>>>> I guess your meaning is:
>>>>>
>>>>>   under arm64, actually, need not support 'VGA_CONSOLE', and 'screen_info' is useless.
>>>>>   So better to define 'CONFIG_HAVE_VGA_CONSOLE' which 'VGA_CONSOLE' can depend on it, and in arm64, we do not define CONFIG_HAVE_VGA_CONSOLE.
>>>>>
>>>>> Is it correct ?
>>> No, you missed "and we can remove the long list of architectures from the
>>> current option".
>>>
>>
>> OK, thanks.
>>
>> Is it correct: "it is unnecessary to add 'screen_info' to the code, for
>> arm64 will never support 'VGA_CONSOLE'" ?
> 
> We can add the screen_info if and when we need to support a VGA console. In
> the meantime, let's not add things on a whim.
> 

OK, thanks. At least now (for our case), need not add 'screen_info', is
it correct ?


>>>>> If so, I recommend to add depend item for VGA_CONSOLE directly:
>>> I strongly support CONFIG_HAVE_VGA_CONSOLE.
>>
>> For me, I still recommend add 'ARM64' in the long list of architectures
>> for 'VGA_CONSOLE', I have 3 reasons, please check:
>>
>> a. current implementation only changes one area which only related with
>> arm64 and 'VGA_CONSOLE', but if use 'CONFIG_HAVE_VGA_CONSOLE', that will
>> touch many multiple platforms dependency, at least we need discuss about
>> it with multiple platforms guys for it, firstly.
> 
> That's a weak argument. You might as well propose the cleanup and see what
> people say.
> 

Hmm.. I think at least, we need discuss it with the 'final applier'
firstly (and now, I even do not know who is the 'final applier').


>> b. We can find some cases to use CONFIG_HAVE_* as dpend on, but I can
>> not find any cases which let CONFIG_'samename' depend on
>> CONFIG_HAVE_'samename'.
> 
> Erm. PERF_EVENTS, BPF_JIT, IDE, ...?
> 

CONFIG_PERF_EVENTS is not directly depend on CONFIG_HAVE_PERF_EVENTS.
CONFIG_BPF_JIT is not directly depend on CONFIG_HAVE_BPF_JIT.
CONFIG_IDE is not directly depend on CONFIG_HAVE_IDE.
...

But I guess what we will do is to let "CONFIG_VGA_CONSOLE is directly
depend on CONFIG_HAVE_VGA_CONSOLE".

So I think we really need discuss it firstly with the 'final applier'.


>> c. The original way still has effect, although it seems not quit
>> beautiful, but it is correct and still clear for readers, it is still
>> sustainable.
> 
> Sure, it works, but we're just contributing to the mess that's been built up
> ever time another architecture has done the same thing. It's not hard to try
> and clean it up.
> 

Can we separate into 2 patches ?. One is for current compiling issue
with allmodconfig (the priority is a litter higher), the other is for
fixup patch (the priority is lower).  ;-)


BTW: In fact, if we really need send the related fixup patch, I am also
unwilling to do that, I guess (in my experience), the fixup patch like
that, will never be applied. :-(


Thanks.
-- 
Chen Gang

Asianux Corporation
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